Surface engineering of LiCoO2 by a multifunctional nanoshell for stable 4.6V electrochemical performance

The 4.6 V LiCoO2 (LCO) cathode is now under intense pursuit, but is challenged by much-aggravated stability issues related to interfacial side reactions and structure degradation. Herein, we demonstrated the possibility to stabilize 4.6 V LCO by building a multifunctional shell of MgO/Li3PO4, which features a mixture of inert MgO and Li+-conductive Li3PO4. Specifically, a wet chemistry route was developed to construct uniform Mg3(PO4)2 nanocoatings with precise thickness control, which were transformed into the desired composite through a surface lithiation process. We found that such a well-tailored surface was not only effective to combat the side reactions, but also critical to facilitate Li+ transfer with much-mitigated polarization, thereby ensuring a stable electrode/electrolyte interface to combat the structural degradation and capacity decay upon long cycles. The surface engineered LCO showed a high reversible capacity of 217.4 mAh g−1 with an outstanding rate capability of 142 mAh g−1 at 10 C. A capacity retention of 79% after 1000 cycles was recorded in the half cell test for the 4.6 V LCO cathode, while 83% of its initial capacity could be remained after 500 cycles in the 4.55 V LCO/graphite pouch full cell. Our results highlighted the essential role played by the surface chemistry on addressing the stability issue of high voltage LCO cathode, and provided useful guidelines for the development of LIBs with higher energy density.